phpize5: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/phpize5 - from package: php5-dev

You may install the required package with command apt-get install {package}

Error in other languages:
phpize5: bevel nie gevind nie
phpize5: comandă negăsită
phpize5: comando não encontrado
phpize5: commande introuvable
phpize5: command not found
phpize5: käsku ei ole
phpize5: không tìm thấy lệnh
phpize5: komanda nerasta
phpize5: Kommando nicht gefunden.
phpize5: kommandot finns inte
phpize5: komut yok
phpize5: nie znaleziono polecenia
phpize5: níor aimsíodh an t-ordú
phpize5: no se encontró la orden
phpize5: no s'ha trobat l'ordre
phpize5: opdracht niet gevonden
phpize5: parancs nem található
phpize5: perintah tidak ditemukan
phpize5: príkaz nenájdený
phpize5: příkaz nenalezen
phpize5: команда не найдена
phpize5: командата не е открита
phpize5: 命令找不到
phpize5: コマンドが見つかりません